It is widely recognized that a link between hair friction and consumer assessments of its visible/tactile characteristics exists. Hair friction is an important physical property, responsible for many visible and tactile characteristics of the hair array. Combing ease is linked to friction and friction also plays a role in how consumers perceive hair conditions and feel.
A widely accepted method for measuring smoothness and softness of hair is combing friction. In practice combing force is measured in the laboratory using a hair switch connected to a load cell. The action of combing, which can be automated or manual stroking, pulls downward on the switch to register a recorded force. In many cases, the hairs being combed will become entangled and cause the comb to snarl and lock as it is pulled through a sample. The only remedy for such entanglement is to use greater force to pull the comb through the tangled sample of hairs. Such forceful pulling causes inconsistencies in measurements and generally requires considerable repetition in order to achieve relatively consistent results.
Another widely used method is generally known as INSTRONO® sled friction. The INSTRON® sled coefficient of friction fixture device is commercially available from INSTRON® as Catalog Number 2810-005. This friction testing method employs an INSTRON® to measure the frictional force as a weighted sled is pulled across the surface of a treated hair bundle. The friction is controlled by the sled surface material (against the hair) and normal force applied. INSTRON® sled friction is generally considered an industry standard when used to compare treatments and evaluate new actives. Nevertheless, this method has demonstrated discrepancies when used to predict or correlate with in vivo consumer use data. This equipment is also too large and impractical to use in vivo, which further prevents such testing from achieving optimal results.
Based on the foregoing, there is a need for a method of assessing the condition of hair in a manner suitable to assess the quality of growing human hair (in vivo). Particularly, there is a need for a method of assessing the condition of hair smoothness and providing consumers with hair treatment recommendations based upon the condition of the hair.